This proposal for the Harvard Informatics Training Program (HITP) recognizes that the field of biomedical informatics is an increasingly relevant, if not essential, field for medicine and research in the health sciences. As such, the primary aim of this proposal is to contribute to the cadre of highly-trained independent and successful researchers in the field of biomedical informatics. Harvard meets all requirements of the current National Library of Medicine (NLM) RFA, which focuses on those basic informatics areas that directly pertain to health-related application domains. The breadth and depth of our research laboratories, real-world clinical systems, research activities, formal academic programs, and experienced faculty provide an outstanding environment to mentor and instruct trainees in all four of the NLM-identified focus areas - healthcare/clinical informatics, translational bioinformatics, clinical research informatics, and public health informatics. Trainees receive in-depth training in foundational informatics methodologies and in each of the focus areas not only in the classroom setting but also through direct experience in the laboratory research setting. Our proposal builds on the strengths of our many years of NLM fellowship training and extends and improves our successful program through three innovations that considerably enhance the program. The HITP program 1) consolidates all of the major Harvard informatics laboratories under the umbrella of the Harvard Center for Biomedical Informatics (CBMI), centrally located on the Harvard Medical School campus, with dedicated space for HITP activities; 2) includes a research seminar - required of all trainees each semester throughout their training - that is a focal point for sustained interactions among all HITP trainees and mentors, regardless of their laboratory setting; 3) provides foundational academic training through the newly established Harvard Medical School Master in Medical Science (MMSc) in Biomedical Informatics. We request support for fifteen NLM trainees each year, 12 at the postdoctoral level and 3 at the predoctoral level. The formal academic component includes the Harvard MMSc for all postdoctoral trainees, and the PhD degree through the MIT Department of Electrical Engineering and Computer Science, with which the Harvard training program has been fully integrated for many years. The HITP program consists of four interrelated components: 1) formal coursework, 2) research mentorship, 3) thesis project, 4) mentored research grant. Trainees' overall progression throughout the training period is closely monitored. Trainees are regularly evaluated through their course work and through progress on their research projects. Progress on the thesis is ensured by the thesis committee, and trainees are regularly encouraged to submit papers for publication.